I am having VERY uneven results when bottling. The beer smells great, tastes great though flat coming out of the secondary fermenter and it is right at target as to final gravity. I bottle it and some bottles are perfect, some are very sweet and a very few have the cider flavor. This is out of the same batch not multiple batches. I have watched the videos, followed the instructions, tried more water with the priming sugar, less water it doesn't seem to matter. In the last 3 months I have had two batches that were all good the remaining 4 were uneven as to results.
I had been reusing bottles so I tried new bottles. I tried 22 ounce bottles and 12 ounce bottles doesn't seem to matter. Some of the higher gravity IPA and Black Ales I have let sit for 6 weeks in the bottle and that helps to even them out but a basic Pale Ale shouldn't take 5 weeks in the bottle.
If they tasted off or were off target on gravity I would say it had to do with my brewing methods but that is not the case as each has been on fg target and tastes good.
So have any of you had a and solved this problem?
Corn Sugar, boiled 10 minutes, siphon from fermentor on top of primer

I only had uneven carbonation on one batch, after that I started stirring gently a few times during the racking process to ensure that the priming sugar mixed thoroughly and evenly with the beer.

Other than that, there's the issue of slow carbonation (which might be the bigger issue since the carbonation seems to even out over time). The usual issue there is low temperature (carbonation will occur more quickly at 70°F or higher), high alcohol (not really an issue with a Pale Ale), or poor yeast health (which also shouldn't be a problem unless the beer is sitting in the fermentor for an unusually long time (maybe more than 2 months) or at unusually high temperatures.

On the other hand, a month isn't that unusual to achieve complete carbonation in a beer that has been racked very cleanly and is held in bottles in the 60sF.

The cidery flavor in some bottles and not others probably indicates a sanitation issue. There's no reason to buy new bottles, but the bottles do need to be clean and sanitized. I recommend washing bottles in something like PBW or Oxyclean. Letting the bottles sit in the cleaner for 10-30 minutes will significantly reduce the amount of living bacteria and fungus in the bottles. Then I suggest using a bottle brush to make sure there is nothing clinging to the bottle and rinsing each bottle well. Then I would suggest using a no-rinse sanitizer, such as StarSan or Iodophore, or heat sanitize in an oven or a dishwasher with a sanitize cycle. Be sure to sanitize the caps as well and avoid touching any surface that will be exposed to beer, such as the inside of the cap or mouth of the bottle, and work in a clean, draft-free room.

I am leaning toward a temperature problem. I keep my carboys covered to keep out light and in a dark corner but the room's ambient temperature can fluctuate as much as 10 degrees. The iffy bottles were fermented during a heat wave and probably contributed to the problem. Does that make sense?

10 degrees is a big fluctuation and a heat wave could have caused problems, I imagine it would depend on what temperatures we were talking about. If it was between 60 and 70F, it could disrupt normal fermentation and slow things down, but probably wouldn't hurt the yeast health in the long term. 75+ during fermentation or maybe 80+ during bottling (I'm not sure what the upper limit is for this, since there's so little fermentation taking place) could potentially lead to off flavors. Any extended period above 80F can be tough on yeast health, though, and will tend to favor bacteria growth that can lead to off-flavors.

It's hard to say, of course, but this is where I would start. Learn what temperatures have worked well for other brewers using that particular yeast (typically the mid-60s for Ale yeasts) and try to control temperatures in that range as well as possible. Luckily, Fall is here and temperature control will get easier.